Brittle microtectonics as defined here is the application of mesofracture analysis to the solution of tectonic problems. For the determination of regionally significant stress or strain trajectories the ideal suite of structures comprises kinematic indicators such as mesofaults, shear zones, arrays of en échelon cracks, kink bands, stylolites and fibrous veins. However, in many tectonic settings joints are the only widespread structures capable of being analysed. The principal criteria for classifying joints into extension, hybrid and shear classes are fracture-system architecture and symmetry, surface morphology, dihedral angles and thin-section characteristics. The architecture of orthogonal extension joints is commonly T-shaped, the younger joint abutting the older one. Neighbouring conjugate hybrid or shear joints generally define X, Y or V shapes but some X patterns are artefacts of unrelated cross-cutting fractures. Conjugate joints enclosing dihedral angles of less than 45° are common; they are interpreted as hybrid failure surfaces initiated in the shear-extension fracture transition. The orientations of many joint sets in platforms are related to far-field stresses generated during plate motion and the subsidence, uplift and inversion of basins. Even within a single joint set there is commonly field evidence to show that it developed during a multiphase failure sequence. Some joints are younger than folds but where a system was established before the close of folding the surfaces commonly become the sites of slip, dilation or pressure solution, and are thus transformed into structures no longer classed as joints.